Membrane filter and filtering method

Abstract

A membrane filter for filtering a liquid to be filtered, the membrane filter including at least one membrane carrier to which membranes are fixed, the membranes allowing a liquid permeate to be filtered out of the liquid, and the membrane carrier includes a permeate collecting chamber to which the membranes are connected in an open manner on the permeate side, and also comprises a permeate outlet for the discharge of the permeate out of the permeate collecting chamber; a gas distribution system which is arranged below the at least one membrane carrier and which has at least one downwardly open and upwardly closed tub which has a wall with downwardly open vertical slots for the distribution of a gas into the liquid to be filtered, at least one gas inlet leading into the gas distribution system. The invention also relates to a method for filtering a liquid.

What is claimed is: 
     
       1. A membrane filter for filtering a liquid, the membrane filter comprising:
 at least one membrane carrier at which membranes are attached which are configured to filter a liquid permeate from the liquid wherein the at least one membrane carrier includes a permeate collecting cavity to which the membranes are connected with an open permeate side of the membranes; 
 a permeate outlet for letting the permeate out from the permeate collecting cavity; 
 a gas distribution system arranged below the at least one membrane carrier and including 
 at least one downward open and upward closed tub which includes a wall with downward open vertical slots for distributing a gas into the liquid, and 
 at least one gas inlet into the gas distribution system, 
 wherein the at least one downward open and upward closed tub includes an inner edge that is arranged between two of the downward open vertical slots that are adjacent to each other in at least one vertical cross section of the at least one downward open and upward closed tub, and 
 wherein each section of the inner edge is oriented at an angle of less than 60° relative to horizontal at least in a portion of a lower half of the downward open vertical slots. 
 
     
     
       2. The membrane filter according to  claim 1 , wherein the gas distribution system is arranged at a bottom side of the at least one membrane carrier. 
     
     
       3. The membrane filter according to  claim 1 ,
 wherein the at least one downward open and upward closed tub includes at least one vertical rib which extends from the wall with the downward open vertical slots in an inward direction of the membrane filter and which is arranged between the two of the downward open vertical slots that are adjacent to each other, and 
 wherein an extension of the at least one vertical rib into the at least one tub decreases in a downward direction. 
 
     
     
       4. The membrane filter according to  claim 1 ,
 wherein the gas distribution system includes downward open gas distribution channels which adjoin at least a portion of the downward open vertical slots on an outside for forwarding and distributing the gas away from the at least one downward open and upward closed tub. 
 
     
     
       5. The membrane filter according to  claim 4 , wherein the gas distribution channels adjoin the downward open vertical slots with a vertical upward offset. 
     
     
       6. The membrane filter according to  claim 1 , wherein the downward open vertical slots become wider in a downward direction. 
     
     
       7. The membrane filter according to claim I, wherein the downward open vertical slots have cross sectional surfaces with different sizes. 
     
     
       8. The membrane filter according to  claim 1 , wherein the at least one gas inlet laterally adjoins the at least one downward open and upward closed tub. 
     
     
       9. A method for filtering a liquid in a membrane filter including
 at least one membrane carrier each having membranes, 
 at least one gas inlet, and 
 a gas distribution system with at least one downward open and upward closed tub which includes a wall with downward open slots, 
 the method comprising the steps: 
 flowing a gas through the at least one gas inlet into the at least one downward open and upward closed tub; 
 filling the at least one downward open and upward closed tub and the downward open slots up to a portion of a height of the downward open slots with a gas cushion formed by the gas; 
 flowing the gas out of the gas cushion through the downward open slots in a laterally outward direction from the at least one downward open and upward closed tub and thus flowing the gas into the liquid at several locations below the at least one membrane carrier; 
 generating a liquid flow caused by the gas at a phase boundary below the gas cushion during a lateral flow of the gas through the downward open slots wherein the liquid flow is parallel to the lateral flow of the gas, 
 generating a rising gas flow in the membrane filter which generates a rising liquid flow in the membrane filter, and 
 flushing the at least one membrane carrier and the membranes attached thereon with the rising liquid flow and the rising gas flow, 
 filtering the liquid through the membranes; and 
 collecting the liquid permeate from the membranes and flowing the liquid permeate out of the membranes; 
 wherein the liquid flow that is generated below the gas cushion flows against an inner edge of the at least one downward open and upward closed tub between adjacent downward open slots in at least one vertical cross section of the at least one downward open and upward closed tub, which cross section is orthogonal to the wall with the downward open slots, 
 wherein the inner edge is oriented at an angle relative to horizontal of less than 60° at least in a portion of a lower half of the downward open slots. 
 
     
     
       10. The method according to  claim 9 , wherein the gas after flowing through some of the downward open slots flows through the gas distribution channels into portions of the membrane filter which are further remote in outward direction than the at least one downward open upward closed tub. 
     
     
       11. The method according to  claim 9 ,
 wherein the gas distribution system is configured at a bottom side of the at least one membrane carrier, and 
 wherein the gas flows around the at least one membrane carrier after flowing into the liquid.